Underlayer film-forming composition and pattern forming process

ABSTRACT

In lithography, a composition comprising a novolak resin comprising recurring units of hydroxycoumarin is used to form a photoresist underlayer film. The underlayer film is strippable in alkaline water, without causing damage to ion-implanted Si substrates or SiO 2  substrates.

CROSS-REFERENCE TO RELATED APPLICATION

This non-provisional application claims priority under 35 U.S.C. §119(a)on Patent Application No. 2013-122866 filed in Japan on Jun. 11, 2013,the entire contents of which are hereby incorporated by reference.

TECHNICAL FIELD

This invention relates to an underlayer film-forming composition and aprocess for forming a pattern in a substrate using the same.

BACKGROUND ART

Recently, CMOS devices are fabricated, in some cases, by performing ionimplantation through a mask of KrF resist film to form p- and n-wells.As the size of resist patterns is reduced, more attention is paid to ArFresist films. For further miniaturization, ArF immersion lithography isproposed. The substrate surface must be bare in spaces of a resist filmbefore ion implantation can be carried out. This is because if a bottomantireflection coating (BARC) layer is present below the resist film,ions are trapped by the BARC layer. However, if the photoresist film ispatterned in the absence of BARC layer, standing waves are generated dueto substrate reflection, resulting in substantial corrugations in thesidewall of resist pattern after development. For the purpose ofsmoothing out a corrugated profile due to standing waves, it is believedeffective to use a photoacid generator (PAG) capable of generating a lowmolecular weight acid amenable to more acid diffusion or to applyhigh-temperature PEB because acid diffusion is enhanced by either means.In the size range of 200 to 300 nm where the resist film for ionimplantation is resolved by KrF lithography, resolution is not degradedby the enhancement of acid diffusion. In the size range of less than 200nm where the resist film for ion implantation is resolved by ArFlithography, however, the enhancement of acid diffusion is undesirablebecause resolution is degraded or proximity bias is enlarged by aciddiffusion.

It was contemplated that the substrate surface to be ion implanted ismade bare by placing a BARC film as a layer beneath a resist film,developing the resist film to form a resist pattern, and dry etching theBARC film with the resist pattern made mask. In this approach, soft dryetching is employed so that the substrate may not be altered, for thereason that if the substrate is oxidized to form an oxide layer, ionscan be trapped by this portion. Specifically, dry etching with hydrogengas is used because the substrate can be oxidized by dry etching withoxygen gas. Then a BARC having a high dry etching rate with hydrogen gasis required.

A dyed resist material is the most traditional technique, which is basedon the concept that a photoresist film itself is made absorptive forpreventing generation of standing waves, and has been investigated sincethe age of i or g-line novolak resist materials. As the absorptivecomponent used in ArF lithography, a study was made on a base polymerhaving benzene ring introduced therein or an additive having benzenering. However, the absorptive component is insufficient to completelyprevent standing waves. Increased absorption is effective for reducingstanding waves, but gives rise to the problem that the resist patternbecomes tapered, i.e., of trapezoidal profile in cross section.

It was also contemplated to provide a top antireflection coating (TARC)film as a layer on the resist film. The TARC is effective for reducingstanding waves, but not for preventing halation due to irregularities onthe substrate. Ideally the refractive index of TARC is equal to thesquare root of the refractive index of the photoresist film. However,since the methacrylate used in the ArF resist film has a relatively lowrefractive index of 1.7 at wavelength 193 nm, there are available nomaterials having a low refractive index equal to its square root, 1.30.

Then a study was made on BARC which is dissolved in developer (see Proc.SPIE Vol. 5039, p 129 (2003)). At the initial, the study was directed toBARC which is anisotropically dissolved in developer. This approach wasdifficult in size control in that with the excess progress ofdissolution, the resist pattern is undercut, and with short dissolution,residuals are left in spaces. Next the study was made on photosensitiveBARC. In order that a film function as BARC, it must have anantireflective effect, remain insoluble in a photoresist solution whichis coated thereon, and avoid intermixing with the photoresist film. Ifthe BARC is crosslinked during post-application bake of BARC solution,it is possible to prevent the BARC from dissolution in the photoresistsolution and intermixing therewith.

As the crosslinking mechanism during post-application bake, JP-AH06-230574 discloses to use vinyl ethers as the crosslinker.Specifically, a vinyl ether crosslinker is blended with hydroxystyrene,whereby crosslinking takes place during prebake after coating, forming aresist film which is insoluble in alkaline developer. Thermal reactionbetween vinyl ether group and phenol group creates an acetal group. ThePAG generates an acid upon exposure. Then the acetal group isdeprotected with the aid of acid, water and heat. The film functions asa positive resist film in that the exposed region is alkali soluble.This mechanism is applicable to dissolvable bottom antireflectioncoating (DBARC) as described in WO 2005/111724 and JP-A 2008-501985.

A substrate to be ion implanted has surface irregularities (or raisedand recessed portions). The BARC becomes thicker on a recessed portionof the substrate. When DBARC is applied to a flat substrate, in theexposed region, the BARC film is dissolved in alkaline developersimultaneously with the photoresist film. When DBARC is applied to astepped substrate, there arises a problem that the DBARC film on therecessed portion is not dissolved. Since DBARC has strong absorption,light does not reach the bottom as the DBARC film becomes thicker, sothat the amount of acid generated by PAG in the DBARC is reduced.Particularly the thicker portion of DBARC film above the step is lesssensitive to light in its proximity to the substrate and thus lessdissolvable.

It is also contemplated to apply the trilayer process to ionimplantation. In this case, a bottom layer of hydrocarbon is coated on asubstrate and crosslinked during bake, a silicon-containing intermediatelayer is coated thereon and crosslinked during bake, and a photoresistmaterial is coated thereon. A resist pattern is formed via exposure anddevelopment. With the resist pattern made mask, the silicon-containingintermediate layer is dry etched with fluorocarbon gas. With thesilicon-containing intermediate layer made mask, the bottom layer isprocessed by dry etching. With the bottom layer made mask, ions areimplanted into the substrate. Although the dry etching for processingthe bottom layer typically uses oxygen gas, dry etching with hydrogengas capable of avoiding oxide formation is preferred for the reason thatthe substrate surface, if oxidized, becomes an ion stop during ionimplantation, as discussed above. The trilayer process can preventreflection off the substrate completely, so that the resist pattern onits sidewall may not be provided with any corrugations due to standingwaves. Where a silsesquioxane-based SOG film is used as thesilicon-containing intermediate layer, the SOG film having a highsilicon content exhibits a high etching rate during dry etching of thesilicon-containing intermediate layer with the resist pattern made maskand a slow etching rate during etching of the bottom layer, that is,exerting an excellent hard mask function, but suffers from the problemthat it is not amenable to solution stripping after ion implantation.While the SOG intermediate layer is typically removed with hydrofluoricacid, the use of hydrofluoric acid causes significant damage to thesubstrate which is a silicon oxide film.

Substrate cleaning solutions which are commonly used in the art includean aqueous solution of ammonia and aqueous hydrogen peroxide (known asSC1), an aqueous solution of hydrochloric acid and aqueous hydrogenperoxide (known as SC2), and an aqueous solution of sulfuric acid andaqueous hydrogen peroxide (known as SPM). Most often, SC1 is used forcleaning of organic matter and metal oxide film, SC2 for removal ofmetal contamination, and SPM for removal of organic film. SOG filmcannot be stripped with these cleaners. The SOG film is removed by dryetching with CF base gas and cleaning with dilute hydrofluoric acid or acombination of dilute hydrofluoric acid and SPM, and the carbonunderlayer film is removed by dry etching with oxygen or hydrogen gas orcleaning with SPM. When oxygen gas etching or SPM solution stripping isapplied to the stripping of the underlayer film on a substrate which isa Si substrate, the substrate surface is oxidized into SiO₂. Once thesurface of Si substrate is converted to SiO₂, the electricalconductivity is reduced to such an extent that the semiconductor may notperform. In contrast, the hydrogen gas etching does not oxidize thesubstrate, but has a slow etching rate, failing to remove phosphorus andarsenic present in the underlayer film after ion implantation. There isa need for an underlayer film which is solution strippable so that anyconcern about oxidation of the substrate surface is eliminated.

CITATION LIST

-   Patent Document 1: JP-A H06-230574 (U.S. Pat. No. 5,939,235, EP    0609684)-   Patent Document 2: WO 2005/111724-   Patent Document 3: JP-A 2008-501985 (WO 2005/093513)-   Patent Document 4: WO 2006/049046-   Patent Document 5: JP-A 2007-017950-   Non-Patent Document 1: Proc. SPIE Vol. 5039, p 129 (2003)

DISCLOSURE OF INVENTION

When the photoresist film is used in the ion implantation process, thesubstrate surface must be bared in the exposed region of resist film atthe time of ion implantation so that ions may be implanted into the bareregion of substrate. Since a silicon substrate is used as the substrate,substantial reflection occurs on the substrate. Although TARC iseffective for suppressing standing waves, it allows some standing wavesto generate because there is not available an optimum low-refractionmaterial capable of completely suppressing standing waves, and it is noteffective for suppressing diffuse reflection (or halation) on anirregular substrate surface. A resist film loaded with an absorbingcomponent has a tendency that if absorption is strong, it is effectivefor suppressing substrate reflection, but the pattern becomes of taperedprofile, and if absorption is weak enough to avoid a tapered profile,the effect of suppressing substrate reflection is reduced so thatcorrugations may result from standing waves. BARC has a very highantireflection effect because reflection is suppressed by two effects,light absorption by an absorber and offset of incident light andreflected light by a choice of an optimum film thickness. However, theBARC surface is bared after development, preventing ion implantationinto the bulk of substrate. Photosensitive DBARC has the problem thatsince it has an increased film thickness on a recessed portion of astepped substrate, this thick film portion is left undissolved. Wherenon-photosensitive BARC is used, the pattern of resist film afterdevelopment may be transferred by dry etching. In this case, the etchingrate of BARC must be higher than that of resist film.

The trilayer process has the problem that when a silsesquioxane base SOGfilm is used as the silicon-containing intermediate film, the SOG filmcannot be stripped without causing damage to the ion implantedsubstrate. A silicon pendant type intermediate film is strippable afterion implantation, but suffers from a low selectivity during dry etchingof the silicon-containing intermediate film with the resist pattern mademask, because of the low silicon content.

Typical of the stripper solution which does not cause the substratesurface to be oxidized is an alkaline aqueous solution. If an underlayerfilm which is strippable with alkaline aqueous solution is available,then it may be stripped without causing damage to the substrate.

Therefore, an object of the invention is to provide an underlayerfilm-forming composition, especially adapted for the ion implantationprocess, which is strippable with basic aqueous solution, typicallyammonia hydrogen peroxide solution, and a pattern forming process usingthe same.

The invention provides an underlayer film-forming composition and apattern forming process, as defined below.

In one aspect, the invention provides a photoresist underlayerfilm-forming composition for use in lithography, comprising a novolakresin comprising recurring units having the general formula (1).

Herein R¹ is hydrogen, an acid labile group, glycidyl group, or astraight, branched or cyclic C₁-C₁₀ alkyl, acyl or alkoxycarbonyl; R² ishydrogen, or a straight, branched or cyclic C₁-C₁₀ alkyl, C₂-C₁₀alkenyl, or C₆-C₁₀ aryl group, which may have a hydroxyl, alkoxy,acyloxy, ether, sulfide or halogen moiety, or a halogen atom, hydroxyl,acyl, carboxyl, acyloxy, alkoxycarbonyl, cyano or C₁-C₄ alkoxy group; R³is hydrogen, or a straight, branched or cyclic C₁-C₆ alkyl, a straight,branched or cyclic C₂-C₁₀ alkenyl, or C₆-C₁₂ aryl group, which may havea hydroxyl, alkoxy, ether, thioether, carboxyl, alkoxycarbonyl, acyloxy,—COOR or —OR moiety, wherein R is a lactone ring, acid labile group, or—R′—COOR″, wherein R′ is a single bond or alkylene group, and R″ is anacid labile group; X is methylene, ethylene, ethynylene, —S— or —NH—;each of m and n is 1 or 2.

In a preferred embodiment, the underlayer film-forming composition mayfurther comprise an organic solvent and more preferably an acidgenerator and/or crosslinker.

In another aspect, the invention provides:

a process for forming a pattern in a substrate by lithography,comprising the steps of applying the underlayer film-forming compositiondefined above onto a substrate to form an underlayer film, forming aphotoresist film on the underlayer film, forming a photoresist patternvia exposure and development, and processing the underlayer film and thesubstrate with the photoresist pattern serving as mask;

a process for forming a pattern in a substrate by lithography,comprising the steps of applying the underlayer film-forming compositiondefined above onto a substrate to form an underlayer film, forming aphotoresist film on the underlayer film, forming a photoresist patternvia exposure and development, processing the underlayer film with thephotoresist pattern serving as mask, and implanting ions into thesubstrate;

a process for forming a pattern in a substrate by lithography,comprising the steps of applying the underlayer film-forming compositiondefined above onto a substrate to form an underlayer film, forming asilicon-containing intermediate film on the underlayer film, forming aphotoresist film on the intermediate film, forming a photoresist patternvia exposure and development, processing the intermediate film with thephotoresist pattern serving as mask, processing the underlayer film withthe intermediate film serving as mask, and processing the substrate withthe underlayer film serving as mask;

a process for forming a pattern in a substrate by lithography,comprising the steps of applying the underlayer film-forming compositiondefined above onto a substrate to form an underlayer film, forming asilicon-containing intermediate film on the underlayer film, forming aphotoresist film on the intermediate film, forming a photoresist patternvia exposure and development, processing the intermediate film with thephotoresist pattern serving as mask, processing the underlayer film withthe intermediate film serving as mask, and implanting ions into thesubstrate with the underlayer film serving as mask.

Preferably, the pattern forming process may further comprise the step ofstripping the underlayer film in alkaline water before or after the stepof processing the substrate.

Also preferably, the pattern forming process may further comprise thestep of stripping the underlayer film in alkaline water after the ionimplantation step.

More preferably the alkaline water is at pH 9 or higher. Typically thealkaline water contains 1 to 99% by weight of at least one memberselected from the group consisting of ammonia, ammonia hydrogen peroxidewater, tetramethylammonium hydroxide, tetraethylammonium hydroxide,tetrapropylammonium hydroxide, tetrabutylammonium hydroxide, cholinehydroxide, benzyltrimethylammonium hydroxide, benzyltriethylammoniumhydroxide, DBU, DBN, hydroxylamine, 1-butyl-1-methylpyrrolidiniumhydroxide, 1-propyl-1-methylpyrrolidinium hydroxide,1-butyl-1-methylpiperidinium hydroxide, 1-propyl-1-methylpiperidiniumhydroxide, mepiquathydroxide, trimethylsulfonium hydroxide, hydrazines,ethylenediamines, and guanidines.

ADVANTAGEOUS EFFECTS OF INVENTION

When a pattern is formed in a substrate by ion implantation, there is aneed for an underlayer film which is strippable without causing damageto the ion implanted substrate. Ideal for the purpose of forming asatisfactory pattern even on an irregular substrate surface bylithography is the trilayer process involving coating a thick underlayerfilm to flatten the topography of the substrate, and coating alight-absorptive silicon-containing intermediate film thereon wherebythe two-layer antireflection coating minimizes substrate reflection.However, after ions are implanted through the pattern formed by thetrilayer process, it is difficult to strip the trilayer without causingdamage to the ion implanted substrate. In contrast, the resistunderlayer film-forming composition of the invention is strippable withalkaline water. A novolak resin having lactone ring, specifically anovolak resin comprising recurring units of hydroxycoumarin ishydrolyzed in alkaline water and converted to hydroxycinnamic acid,i.e., to generate a carboxyl group so that the resin turns soluble inalkaline aqueous solution. Thus the underlayer film can be strippedwithout causing damage to the ion implanted Si or SiO₂ substrate.

BRIEF DESCRIPTION OF DRAWINGS

FIGS. 1A-D are a set of cross-sectional views illustrating former stepsof the pattern forming process according to one embodiment of theinvention, FIG. 1A showing a hydrocarbon underlayer film formed on asubstrate, FIG. 1B showing a silicon-containing intermediate film formedthereon, FIG. 1C showing a resist film formed thereon, and FIG. 1Dshowing exposure of the resist film.

FIGS. 2E-H are a set of cross-sectional views illustrating later stepsof the pattern forming process, FIG. 2E showing the steps of PEB andalkaline development, FIG. 2F showing the step of processing thehydrocarbon underlayer film with H₂ gas with the silicon-containingintermediate film made mask, FIG. 2G showing the step of ionimplantation with the hydrocarbon underlayer film made mask, and FIG. 2Hshowing the substrate after the silicon-containing intermediate film andhydrocarbon underlayer film have been stripped off.

DESCRIPTION OF PREFERRED EMBODIMENTS

In the disclosure, the singular forms “a,” “an” and “the” include pluralreferents unless the context clearly dictates otherwise. The notation(Cn-Cm) means a group containing from n to m carbon atoms per group. Asused herein, the term “underlayer” refers to a layer under the resistfilm.

The abbreviations and acronyms have the following meaning.

Mw: weight average molecular weight

Mn: number average molecular weight

Mw/Mn: molecular weight distribution or dispersity

GPC: gel permeation chromatography

PEB: post-exposure bake

BARC: bottom antireflective coating

PAG: photoacid generator

The inventors made efforts to develop a resist underlayer film-formingcomposition which can be stripped with alkaline water, especiallyammonia hydrogen peroxide solution, after ion implantation. To this end,a material which is hydrolyzable with ammonia to generate a carboxyl orsulfo group so that its alkali dissolution rate is improved ispreferred. Such materials include novolak resins having lactone ring,typically hydroxycoumarin. While lactones and acid anhydrides generate acarboxyl group upon hydrolysis, these materials are less resistant todry etching. In order that a film be used as an underlayer film in thetrilayer process or ion implantation process, the film must have anaccordingly high level of dry etching resistance and ion implantationresistance. For such resistance, the material must have an aromaticgroup. Although it may be contemplated to use an underlayer film-formingmaterial consisting of a hydroxycoumarin or analogous monomer, theunderlayer film composed of the monomeric material has a possibilitythat when a photoresist solution or a silicon-containing intermediatefilm solution is coated thereon, the underlayer film is dissolved inthese solutions, with the risk of intermixing. To avoid the risk, apolymer containing hydroxycoumarin or analog must be used. Mostadvantageously, the polymer should take the form of a novolak resinresulting from polymerization with an aldehyde.

Based on the foregoing considerations, the inventors have found that aresist underlayer (antireflective) film-forming composition comprising anovolak resin comprising at least recurring units derived from asubstituted or unsubstituted hydroxycoumarin or lactone ring-bearinganalogs is advantageous in that the underlayer film formed therefrom hashigh dry etching resistance and ion implantation resistance and isstrippable with alkaline water after dry etching or after ionimplantation.

In one aspect, the invention is directed to a composition for forming aphotoresist underlayer film for use in lithography, the underlayerfilm-forming composition comprising a novolak resin comprising recurringunits having the general formula (1).

Herein R¹ is hydrogen, an acid labile group, glycidyl group, or astraight, branched or cyclic C₁-C₁₀, especially C₁-C₆ alkyl, acyl oralkoxycarbonyl. R² is hydrogen, or a straight, branched or cyclicC₁-C₁₀, especially C₁-C₆ alkyl, C₂-C₁₀, especially C₂-C₆ alkenyl, orC₆-C₁₀ aryl group, which may have a hydroxyl, alkoxy, acyloxy, ether,sulfide or halogen moiety, or a halogen atom, hydroxyl, acyl, carboxyl,acyloxy, alkoxycarbonyl, cyano or C₁-C₄ alkoxy group. R³ is hydrogen, ora straight, branched or cyclic C₁-C₆ alkyl, a straight, branched orcyclic C₂-C₁₀, especially C₂-C₆ alkenyl, or C₆-C₁₂, especially C₆-C₁₀aryl group, which may have a hydroxyl, alkoxy (especially C₁-C₄ alkoxy),ether, thioether, carboxyl, alkoxycarbonyl (especially C₁-C₆alkoxycarbonyl), acyloxy, —COOR or —OR moiety, wherein R is a lactonering, acid labile group, or —R′—COOR″, wherein R′ is a single bond oralkylene group, and R″ is an acid labile group. X is methylene,ethylene, ethynylene, —S— or —NH—. Each of m and n is 1 or 2.

It is noted that the alkenyl groups having an ether or thioether moietyare shown below.

Examples of the monomer from which the novolak resin comprisingrecurring units of formula (1) is derived are illustrated below, but notlimited thereto.

When novolak resins are derived from a substituted or unsubstitutedhydroxycoumarin, it may be co-condensed with another monomer ormonomers. Examples of the co-condensable monomer include, but are notlimited to, phenolphthalein, Phenol Red, Cresolphthalein, Cresol Red,Thymolphthalein, naphtholphthalein, fluorescein, phenol, o-cresol,m-cresol, p-cresol, 2,3-dimethylphenol, 2,5-dimethylphenol,3,4-dimethylphenol, 3,5-dimethylphenol, 2,4-dimethylphenol,2,6-dimethylphenol, 2,3,5-trimethylphenol, 3,4,5-trimethylphenol,2-tert-butylphenol, 3-tert-butylphenol, 4-tert-butylphenol,2-phenylphenol, 3-phenylphenol, 4-phenylphenol, 3,5-diphenylphenol,2-naphthylphenol, 3-naphthylphenol, 4-naphthylphenol, 4-tritylphenol,resorcinol, 2-methylresorcinol, 4-methylresorcinol, 5-methylresorcinol,catechol, 4-tert-butylcatechol, 2-methoxyphenol, 3-methoxyphenol,2-propylphenol, 3-propylphenol, 4-propylphenol, 2-isopropylphenol,3-isopropylphenol, 4-isopropylphenol, 2-methoxy-5-methylphenol,2-tert-butyl-5-methylphenol, pyrogallol, thymol, isothymol,4,4′-(9H-fluoren-9-ylidene)bisphenol,2,2′-dimethyl-4,4′-(9H-fluoren-9-ylidene)bisphenol,2,2′-diallyl-4,4′-(9H-fluoren-9-ylidene)bisphenol,2,2′-difluoro-4,4′-(9H-fluoren-9-ylidene)bisphenol,2,2′-diphenyl-4,4′-(9H-fluoren-9-ylidene)bisphenol,2,2′-dimethoxy-4,4′-(9H-fluoren-9-ylidene)bisphenol,2,3,2′,3′-tetrahydro-(1,1′)-spirobiindene-6,6′-diol,3,3,3′,3′-tetramethyl-2,3,2′,3′-tetrahydro-(1,1′)-spirobiindene-6,6′-diol,3,3,3′,3′,4,4′-hexamethyl-2,3,2′,3′-tetrahydro-(1,1′)-spirobiindene-6,6′-diol,2,3,2′,3′-tetrahydro-(1,1′)-spirobiindene-5,5′-diol,5,5′-dimethyl-3,3,3′,3′-tetramethyl-2,3,2′,3′-tetrahydro-(1,1′)-spirobiindene-6,6′-diol,1,2-dihydroxynaphthalene, 1,3-dihydroxynaphthalene,1,4-dihydroxynaphthalene, 1,5-dihydroxynaphthalene,1,6-dihydroxynaphthalene, 1,7-dihydroxynaphthalene,1,8-dihydroxynaphthalene, 2,3-dihydroxynaphthalene,2,4-dihydroxynaphthalene, 2,5-dihydroxynaphthalene,2,6-dihydroxynaphthalene, 2,7-dihydroxynaphthalene, and2,8-dihydroxynaphthalene. Examples of the compound which can beco-condensed with dihydroxynaphthalene include 1-naphthol, 2-naphthol,2-methyl-1-naphthol, 4-methoxy-1-naphthol, 7-methoxy-2-naphthol,6-methoxy-2-naphthol, 3-methoxy-2-naphthol, 1,4-dimethoxynaphthalene,1,5-dimethoxynaphthalene, 1,6-dimethoxynaphthalene,1,7-dimethoxynaphthalene, 1,8-dimethoxynaphthalene,2,3-dimethoxynaphthalene, 2,6-dimethoxynaphthalene,2,7-dimethoxynaphthalene, methyl 3-hydroxy-naphthalene-2-carboxylate,naphthalene, 1-methylnaphthalene, 2-methylnaphthalene,1,2-dimethylnaphthalene, 1,3-dimethylnaphthalene,1,4-dimethylnaphthalene, 1,5-dimethylnaphthalene,1,6-dimethylnaphthalene, 1,7-dimethylnaphthalene,1,8-dimethylnaphthalene, 2,3-dimethylnaphthalene,2,6-dimethylnaphthalene, 2,7-dimethylnaphthalene, 1-ethylnaphthalene,2-ethylnaphthalene, 1-propylnaphthalene, 2-propylnaphthalene,1-butylnaphthalene, 2-butylnaphthalene, 1-phenylnaphthalene,1-cyclohexylnaphthalene, 1-cyclopentylnaphthalene, 1,1′-bi(2-naphthol),o-cresol, m-cresol, p-cresol, indene, hydroxyanthracene, acenaphthylene,acenaphthene, biphenyl, bisphenol, trisphenol, dicyclopentadiene,1,5-dimethylnaphthalene, and 6,6′-(9H-fluoren-9-ylidene)bis-2-naphthol.

The monomer to be co-condensed may be contained in an amount of 0 to 80mol %.

Upon polymerization of a substituted or unsubstituted hydroxycoumarin,aldehydes are added thereto to form novolak resins. Novolak conversionbrings about a molecular weight buildup, thus controlling outgassing orparticle formation from a low molecular weight fraction during bake.Examples of the aldehyde used herein include formaldehyde, trioxane,paraformaldehyde, benzaldehyde, methoxybenzaldehyde, phenylbenzaldehyde,tritylbenzaldehyde, cyclohexylbenzaldehyde, cyclopentylbenzaldehyde,tert-butylbenzaldehyde, naphthalene aldehyde, hydroxynaphthalenealdehyde, anthracene aldehyde, fluorene aldehyde, pyrene aldehyde,methoxynaphthalene aldehyde, dimethoxynaphthalene aldehyde,acetaldehyde, propyl aldehyde, phenylacetaldehyde, naphthaleneacetaldehyde, substituted or unsubstituted carboxynaphthaleneacetaldehyde, α-phenylpropyl aldehyde, β-phenylpropyl aldehyde,o-hydroxybenzaldehyde, m-hydroxybenzaldehyde, p-hydroxybenzaldehyde,o-chlorobenzaldehyde, m-chlorobenzaldehyde, p-chlorobenzaldehyde,o-nitrobenzaldehyde, m-nitrobenzaldehyde, p-nitrobenzaldehyde,o-methylbenzaldehyde, m-methylbenzaldehyde, p-methylbenzaldehyde,p-ethylbenzaldehyde, p-n-butylbenzaldehyde, furfural,furancarboxyaldehyde, and thiophene aldehyde. Inter alia, formaldehydeis most preferred. These aldehydes may be used alone or in combinationof two or more.

An appropriate amount of the aldehyde used is 0.2 to 5 moles, morepreferably 0.5 to 2 moles per mole of the hydroxycoumarin.

A catalyst may be used in the condensation reaction of hydroxycoumarinwith an aldehyde(s). Suitable catalysts are acidic catalysts such ashydrochloric acid, nitric acid, sulfuric acid, formic acid, oxalic acid,acetic acid, methanesulfonic acid, camphorsulfonic acid, tosylic acid,and trifluoromethanesulfonic acid. An appropriate amount of the acidiccatalyst used is 1×10⁻⁵ to 5×10⁻¹ mole per mole of the hydroxycoumarin.

The novolak resin comprising recurring units of hydroxycoumarin shouldpreferably have a weight average molecular weight (Mw) of 400 to 20,000,as measured by GPC versus polystyrene standards. Mw is more preferablyin a range of 500 to 10,000, even more preferably 600 to 10,000. Since aresin having a lower molecular weight has better burying properties, butis more likely to outgassing during bake, the Mw is preferably optimizedfor a balance of burying and outgassing. One measure for meeting bothburying ability and outgassing reduction is to cut off unpolymerizedhydroxycoumarin as much as possible and preferably to minimize theamount of a low molecular weight fraction including dimer and trimer.

In formulating the hydrocarbon underlayer film-forming composition, thenovolak resin comprising recurring units of hydroxycoumarin may beblended with another resin. Suitable resins which can be blended arenovolak resins obtained from reaction of phenols or analogs withaldehydes, with suitable phenols and analogs including phenolphthalein,Phenol Red, Cresolphthalein, Cresol Red, Thymolphthalein,naphtholphthalein, fluorescein, phenol, o-cresol, m-cresol, p-cresol,2,3-dimethylphenol, 2,5-dimethylphenol, 3,4-dimethylphenol,3,5-dimethylphenol, 2,4-dimethylphenol, 2,6-dimethylphenol,2,3,5-trimethylphenol, 3,4,5-trimethylphenol, 2-tert-butylphenol,3-tert-butylphenol, 4-tert-butylphenol, 2-phenylphenol, 3-phenylphenol,4-phenylphenol, 3,5-diphenylphenol, 2-naphthylphenol, 3-naphthylphenol,4-naphthylphenol, 4-tritylphenol, resorcinol, 2-methylresorcinol,4-methylresorcinol, 5-methylresorcinol, catechol, 4-tert-butylcatechol,2-methoxyphenol, 3-methoxyphenol, 2-propylphenol, 3-propylphenol,4-propylphenol, 2-isopropylphenol, 3-isopropylphenol, 4-isopropylphenol,2-methoxy-5-methylphenol, 2-tert-butyl-5-methylphenol, pyrogallol,thymol, isothymol, 1-naphthol, 2-naphthol, 2-methyl-1-naphthol,4-methoxy-1-naphthol, 7-methoxy-2-naphthol, dihydroxynaphthalenes (e.g.,1,5-dihydroxynaphthalene, 1,7-dihydroxynaphthalene,2,6-dihydroxynaphthalene), methyl 3-hydroxy-naphthalene-2-carboxylate,indene, hydroxyindene, benzofuran, hydroxyanthracene, acenaphthylene,biphenyl, bisphenol, and trisphenol. Also useful are resins obtainedfrom copolymerization of a phenol with dicyclopentadiene,tetrahydroindene, 4-vinylcyclohexene, norbornadiene,5-vinylnorborn-2-ene, α-pinene, β-pinene or limonene, but withoutaldehydes.

The underlayer film-forming composition may further comprise a polymerobtained from polymerization of a monomer selected from amonghydroxystyrene, alkoxystyrenes, hydroxyvinylnaphthalene,alkoxyvinylnaphthalenes, (meth)acrylates, vinyl ethers, maleicanhydride, and itaconic anhydride. It is also acceptable to add amonomer form of phenolphthalein, Phenol Red, Cresolphthalein, CresolRed, Thymolphthalein, naphtholphthalein or fluorescein to thecomposition.

While various high-carbon resins may be added to the underlayerfilm-forming composition, exemplary high-carbon resins are described inthe following patents.

-   -   JP-A 2004-205658, JP-A 2004-205676, JP-A 2004-205685, JP-A        2004-271838, JP-A 2004-354554, JP-A 2005-010431, JP-A        2005-049810, JP-A 2005-114921, JP-A 2005-128509, JP-A        2005-250434, JP-A 2006-053543, JP-A 2006-227391, JP-A        2006-259249, JP-A 2006-259482, JP-A 2006-285095, JP-A        2006-293207, JP-A 2006-293298, JP-A 2007-140461, JP-A        2007-171895, JP-A 2007-199653, JP-A 2007-316282, JP-A        2008-026600, JP-A 2008-065303, JP-A 2008-096684, JP-A        2008-116677, JP-A 2008-145539, JP-A 2008-257188, JP-A        2010-160189, JP-A 2010-134437, JP-A 2010-170013, and JP-A        2010-271654.

The amount of the other resin may be 0 to 300 parts by weight.

While R¹, R², R, and R″ stand for an acid labile group, the acid labilegroups may be identical or different and preferably include groups ofthe following formulae (A-1) to (A-3).

In formula (A-1), R^(L30) is a tertiary alkyl group of 4 to 20 carbonatoms, preferably 4 to 15 carbon atoms, a trialkylsilyl group in whicheach alkyl moiety has 1 to 6 carbon atoms, an oxoalkyl group of 4 to 20carbon atoms, or a group of formula (A-3). Exemplary tertiary alkylgroups are tert-butyl, tert-amyl, 1,1-diethylpropyl, 1-ethylcyclopentyl,1-butylcyclopentyl, 1-ethylcyclohexyl, 1-butylcyclohexyl,1-ethyl-2-cyclopentenyl, 1-ethyl-2-cyclohexenyl, and2-methyl-2-adamantyl. Exemplary trialkylsilyl groups are trimethylsilyl,triethylsilyl, and dimethyl-tert-butylsilyl. Exemplary oxoalkyl groupsare 3-oxocyclohexyl, 4-methyl-2-oxooxan-4-yl, and5-methyl-2-oxooxolan-5-yl. Letter A1 is an integer of 0 to 6.

In formula (A-2), R^(L31) and R^(L32) each are hydrogen or a straight,branched or cyclic alkyl group of 1 to 18 carbon atoms, preferably 1 to10 carbon atoms. Exemplary alkyl groups include methyl, ethyl, propyl,isopropyl, n-butyl, sec-butyl, tert-butyl, cyclopentyl, cyclohexyl,2-ethylhexyl, and n-octyl. R^(L33) is a monovalent hydrocarbon group of1 to 18 carbon atoms, preferably 1 to 10 carbon atoms, which may containa heteroatom such as oxygen, examples of which include straight,branched or cyclic alkyl groups and substituted forms of such alkylgroups in which some hydrogen atoms are replaced by hydroxyl, alkoxy,oxo, amino, alkylamino or the like. Illustrative examples of thesubstituted alkyl groups are shown below.

A pair of R^(L31) and R^(L32), R^(L31) and R^(L33), or R^(L32) and R maybond together to form a ring with the carbon and oxygen atoms to whichthey are attached. Each of R^(L31), R^(L32) and R^(L33) is a straight orbranched alkylene group of 1 to 18 carbon atoms, preferably 1 to 10carbon atoms when they form a ring, while the ring preferably has 3 to10 carbon atoms, more preferably 4 to 10 carbon atoms.

Examples of the acid labile groups of formula (A-1) includetert-butoxycarbonyl, tert-butoxycarbonylmethyl, tert-amyloxycarbonyl,tert-amyloxycarbonylmethyl,

-   1,1-diethylpropyloxycarbonyl,-   1,1-diethylpropyloxycarbonylmethyl,-   1-ethyl cyclopentyloxycarbonyl,-   1-ethylcyclopentyloxycarbonylmethyl,-   1-ethyl-2-cyclopentenyloxycarbonyl,-   1-ethyl-2-cyclopentenyloxycarbonylmethyl,-   1-ethoxyethoxycarbonylmethyl,-   2-tetrahydropyranyloxycarbonylmethyl, and-   2-tetrahydrofuranyloxycarbonylmethyl groups.    Also included are substituent groups having the formulae (A-1)-1 to    (A-1)-10.

Herein R^(L37) is each independently a straight, branched or cyclicC₁-C₁₀ alkyl group or C₆-C₂₀ aryl group. R^(L38) is hydrogen or astraight, branched or cyclic C₁-C₁₀ alkyl group. R^(L39) is eachindependently a straight, branched or cyclic C₂-C₁₀ alkyl group orC₆-C₂₀ aryl group. A1 is an integer of 0 to 6.

Of the acid labile groups of formula (A-2), the straight and branchedones are exemplified by the following groups having formulae (A-2)-1 to(A-2)-69.

Of the acid labile groups of formula (A-2), the cyclic ones are, forexample, tetrahydrofuran-2-yl, 2-methyltetrahydrofuran-2-yl,tetrahydropyran-2-yl, and 2-methyltetrahydropyran-2-yl.

Other examples of acid labile groups include those of the followingformula (A-2a) or (A-2b) while the polymer (base resin) may becrosslinked within the molecule or between molecules with these acidlabile groups.

Herein R^(L40) and R^(L41) each are hydrogen or a straight, branched orcyclic C₁-C₈ alkyl group, or R^(L40) and R^(L41), taken together, mayform a ring with the carbon atom to which they are attached, and R^(L40)and R^(L41) are straight or branched C₁-C₈ alkylene groups when theyform a ring. R^(L42) is a straight, branched or cyclic C₁-C₁₀ alkylenegroup. Each of B1 and D1 is 0 or an integer of 1 to 10, preferably 0 oran integer of 1 to 5, and C1 is an integer of 1 to 7. “A” is a(C1+1)-valent aliphatic or alicyclic saturated hydrocarbon group,aromatic hydrocarbon group or heterocyclic group having 1 to 50 carbonatoms, which may be separated by a heteroatom or in which some hydrogenatoms attached to carbon atoms may be substituted by hydroxyl, carboxyl,carbonyl groups or fluorine atoms. “B” is —CO—O—, —NHCO—O— or —NHCONH—.

Preferably, “A” is selected from divalent to tetravalent, straight,branched or cyclic C₁-C₂₀ alkylene, alkyltriyl and alkyltetrayl groups,and C₆-C₃₀ arylene groups, which may contain a heteroatom or in whichsome hydrogen atoms attached to carbon atoms may be substituted byhydroxyl, carboxyl, acyl groups or halogen atoms. The subscript C1 ispreferably an integer of 1 to 3.

The crosslinking acetal groups of formulae (A-2a) and (A-2b) areexemplified by the following formulae (A-2)-70 through (A-2)-77.

In formula (A-3), R^(L34), R^(L35) and R^(L36) each are a monovalenthydrocarbon group, typically a straight, branched or cyclic C₁-C₂₀ alkylgroup or a straight, branched or cyclic C₂-C₂₀ alkenyl group, which maycontain a heteroatom such as oxygen, sulfur, nitrogen or fluorine. Apair of R^(L34) and R^(L35), R^(L34) and R^(L36), or R^(L35) and R^(L36)may bond together to form a C₃-C₂₀ ring with the carbon atom to whichthey are attached.

Exemplary tertiary alkyl groups of formula (A-3) include tert-butyl,triethylcarbyl, 1-ethylnorbornyl, 1-methylcyclohexyl,1-ethylcyclopentyl, 2-(2-methyl)adamantyl, 2-(2-ethyl)adamantyl, andtert-amyl.

Other exemplary tertiary alkyl groups include those of the followingformulae (A-3)-1 to (A-3)-18.

Herein R^(L43) is each independently a straight, branched or cyclicC₁-C₈ alkyl group or C₆-C₂₀ aryl group, typically phenyl. R^(L44) andR^(L46) each are hydrogen or a straight, branched or cyclic C₁-C₂₀ alkylgroup. R^(L45) is a C₆-C₂₀ aryl group, typically phenyl.

The polymer may be crosslinked within the molecule or between moleculeswith groups having R^(L47) which is a di- or multi-valent alkylene orarylene group, as shown by the following formulae (A-3)-19 and (A-3)-20.

Herein R^(L43) is as defined above. R^(L47) is a straight, branched orcyclic C₁-C₂₀ alkylene group or arylene group, typically phenylene,which may contain a heteroatom such as oxygen, sulfur or nitrogen. E1 isan integer of 1 to 3.

The novolak resin comprising recurring units of formula (1) is adaptedto generate a carboxyl or sulfo group in a basic aqueous solution,typically ammonia hydrogen peroxide solution. Then the resin turnsalkali soluble so that the film may be stripped with ammonia hydrogenperoxide solution.

The resist underlayer film must have the nature that when asilicon-containing intermediate film solution or resist solution isdispensed on the underlayer film, the underlayer film is neitherdissolved in such solution nor mixed with such solution. To this end,the underlayer film must be crosslinked during post-application bake. Inthis regard, the underlayer film-forming composition should preferablyfurther comprise a crosslinker.

Examples of the crosslinker which can be used herein include melaminecompounds, guanamine compounds, glycoluril compounds and urea compoundshaving substituted thereon at least one group selected from amongmethylol, alkoxymethyl and acyloxymethyl groups, epoxy compounds,isocyanate compounds, azide compounds, and compounds having a doublebond such as an alkenyl ether group. These compounds may be used as anadditive or introduced as pendant groups on polymer side chains.Compounds having a hydroxy group are also useful as the crosslinker.

Of the foregoing crosslinkers, examples of suitable epoxy compoundsinclude tris(2,3-epoxypropyl)isocyanurate, trimethylolmethanetriglycidyl ether, trimethylolpropane triglycidyl ether, andtriethylolethane triglycidyl ether. Examples of the melamine compoundinclude hexamethylol melamine, hexamethoxymethyl melamine, hexamethylolmelamine compounds having 1 to 6 methylol groups methoxymethylated andmixtures thereof, hexamethoxyethyl melamine, hexaacyloxymethyl melamine,hexamethylol melamine compounds having 1 to 6 methylol groupsacyloxymethylated and mixtures thereof. Examples of the guanaminecompound include tetramethylol guanamine, tetramethoxymethyl guanamine,tetramethylol guanamine compounds having 1 to 4 methylol groupsmethoxymethylated and mixtures thereof, tetramethoxyethyl guanamine,tetraacyloxyguanamine, tetramethylol guanamine compounds having 1 to 4methylol groups acyloxymethylated and mixtures thereof. Examples of theglycoluril compound include tetramethylol glycoluril,tetramethoxyglycoluril, tetramethoxymethyl glycoluril, tetramethylolglycoluril compounds having 1 to 4 methylol groups methoxymethylated andmixtures thereof, tetramethylol glycoluril compounds having 1 to 4methylol groups acyloxymethylated and mixtures thereof. Examples of theurea compound include tetramethylol urea, tetramethoxymethyl urea,tetramethylol urea compounds having 1 to 4 methylol groupsmethoxymethylated and mixtures thereof, and tetramethoxyethyl urea.

Examples of the isocyanate compound include tolylene diisocyanate,diphenylmethane diisocyanate, hexamethylene diisocyanate, andcyclohexane diisocyanate. Examples of the azide compound include1,1′-biphenyl-4,4′-bisazide, 4,4′-methylidene bisazide and4,4′-oxybisazide.

Suitable crosslinkers capable of crosslinking with an acetal groupinclude compounds having a plurality of enol ether groups in themolecule. Suitable crosslinkers having two or more enol ether groups inthe molecule include ethylene glycol divinyl ether, triethylene glycoldivinyl ether, 1,2-propanediol divinyl ether, 1,4-butanediol divinylether, tetramethylene glycol divinyl ether, neopentyl glycol divinylether, trimethylol propane trivinyl ether, hexanediol divinyl ether,1,4-cyclohexanediol divinyl ether, pentaerythritol trivinyl ether,pentaerythritol tetravinyl ether, sorbitol tetravinyl ether, sorbitolpentavinyl ether, trimethylol propane trivinyl ether, ethylene glycoldipropenyl ether, triethylene glycol dipropenyl ether, 1,2-propanedioldipropenyl ether, 1,4-butanediol dipropenyl ether, tetramethylene glycoldipropenyl ether, neopentyl glycol dipropenyl ether, trimethylol propanetripropenyl ether, hexanediol dipropenyl ether, 1,4-cyclohexanedioldipropenyl ether, pentaerythritol tripropenyl ether, pentaerythritoltetrapropenyl ether, sorbitol tetrapropenyl ether, sorbitolpentapropenyl ether, trimethylolpropane tripropenyl ether, and thosedescribed in JP-A H06-230574, JP-A 2007-536389, and JP-A 2008-501985.

Also useful are crosslinkers as shown below.

Upon application of heat, the enol ether group forms an acetal bond witha hydroxyl group. Therefore, when a compound having a plurality of enolether groups per molecule is added, thermal crosslinking takes place viaacetal groups.

Also useful is a crosslinker having an acid labile tertiary ester groupand containing at least two oxirane rings in the molecule. Suchcrosslinkers are described in JP-A 2006-096848. The oxirane ring forms acrosslink by heat and the tertiary ester group is decomposed with acid.JP-A 2001-226430 discloses the thermal crosslinking of oxirane ring andthe acid-aided decomposition mechanism.

In the hydrocarbon-based underlayer film-forming composition of theinvention, the crosslinker is preferably compounded in an amount of 0 to50 parts, more preferably 5 to 50 parts, and even more preferably 10 to40 parts by weight per 100 parts by weight of the base polymer (totalresins). Less than 5 parts of the crosslinker may leave the risk ofintermixing with the resist film whereas more than 50 parts of thecrosslinker may adversely affect the antireflection effect and permitthe crosslinked film to crack.

On the underlayer film formed of the composition mentioned above, aphotoresist film is formed in one embodiment. In another embodimentcorresponding to the trilayer process, a photoresist film is formed onthe underlayer film and an intermediate layer is formed between thephotoresist film and the underlayer film. The trilayer process ispreferred. The intermediate layer contains a metal selected fromsilicon, titanium, zirconium, hafnium and the like. Of these, silicon isthe most preferred element in the intermediate layer.

Where the trilayer process is applied to the pattern formationtechnology by ion implantation, not only stripping of the underlayerfilm, but also stripping of the intermediate layer after ionimplantation are considerations. Where a SOG film is used as theintermediate layer, fluorocarbon based gas is used to strip the SOG filmby dry process, but the etching with fluorocarbon based gas can causedamage to the underlying oxide film. The SOG film may also be strippedusing an aqueous solution of hydrofluoric acid, but the underlying oxidefilm is simultaneously stripped with this solution. It is thus necessaryto strip the intermediate layer and underlayer film using an acid oralkali or a solvent. The intermediate layer which can be stripped withthe acid or alkali is preferably a layer based on a polymer havingsilicon pendants, more preferably an acid labile group-bearing siliconpendant polymer. Then the intermediate layer can be stripped in anacceptable manner.

The acid labile group-bearing silicon pendant polymer is preferablydefined as comprising recurring units of the general formula (2).

Herein, R¹¹ is hydrogen or methyl. R¹², R¹³, R¹⁴, and R¹⁵ are eachindependently hydrogen or a straight or branched C₁-C₄ alkyl group. R¹⁶is a single bond or a dialkylsilylene group. R¹⁷, R¹⁸, R¹⁹, R²⁰, and R²¹are each independently hydrogen, a straight, branched or cyclic C₁-C₂₀alkyl group, a C₆-C₂₀ aryl group, or a group of the general formula (3)shown below. Alternatively, R¹⁷, R¹⁸, R¹⁹, R²⁰, and R²¹ may bondtogether to form a ring.

In formula (3), R²², R²³, R²⁴, R²⁵, and R²⁶ are each independentlyhydrogen, a straight, branched or cyclic C₁-C₂₀ alkyl group or a C₆-C₂₀aryl group, and t is a number of 0 to 10 (0≦t≦10).

The polymer for use in the silicon-containing intermediate film-formingcomposition may be synthesized, for example, by dissolving a monomer(s)in an organic solvent, adding a radical or cation polymerizationinitiator thereto, and effecting heat polymerization. Where ahydroxyl-containing monomer is used, the hydroxyl group on the monomermay be previously substituted by an acetyl group, and the resultingpolymer be subjected to alkaline hydrolysis in the organic solventwhereby the acetyl group is deprotected. Examples of the organic solventwhich can be used for polymerization include toluene, benzene,tetrahydrofuran, diethyl ether and dioxane. Examples of the radicalpolymerization initiator used herein include 2,2′-azobisisobutyronitrile(AIBN), 2,2′-azobis(2,4-dimethylvaleronitrile), dimethyl2,2-azobis(2-methylpropionate), benzoyl peroxide, and lauroyl peroxide.Preferably the system is heated at 50 to 80° C. for polymerization totake place. Examples of the cation polymerization initiator used hereininclude acids such as sulfuric acid, phosphoric acid, hydrochloric acid,nitric acid, hypochlorous acid, trichloroacetic acid, trifluoroaceticacid, methanesulfonic acid, trifluoromethanesulfonic acid,camphorsulfonic acid, and tosylic acid; Friedel-Crafts catalysts such asBF₃, AlCl₃, TiCl₄ and SnCl₄; and cation-providing substances such as I₂and (C₆H₅)₃CCl. The reaction time is 2 to 100 hours, preferably 5 to 20hours.

For alkaline hydrolysis, a base such as aqueous ammonia or triethylaminemay be used. The reaction temperature is −20° C. to 100° C., preferably0° C. to 60° C., and the reaction time is 0.2 to 100 hours, preferably0.5 to 20 hours.

Preferably the polymer for use in the intermediate film-forming materialhas a weight average molecular weight in the range of 1,500 to 200,000,more preferably 2,000 to 100,000 as measured versus polystyrenestandards by GPC. The molecular weight distribution or dispersity is notcritical. If desired, lower and higher molecular weight fractions can beremoved by fractionation for reducing the dispersity. It is acceptableto use a mixture of two or more polymers of formula (2) having differentmolecular weights or dispersities or a mixture of two or more polymersof formula (2) having different compositional ratios.

Both the hydrocarbon-based resist underlayer film-forming compositionand the silicon-containing intermediate film-forming composition mayfurther comprise an acid generator for further promoting heat- orotherwise induced crosslinking reaction. While the acid generatorsinclude those capable of generating acid by pyrolysis and those capableof generating acid upon radiation exposure, either one may be usedherein.

The acid generator to be added to the intermediate film may be aphotoacid generator (PAG) so that the exposed region of the film maybecome dissolved in alkaline developer. In this case, preference isgiven to a PAG having so high thermal stability that it may not bedecomposed during post-application bake (for crosslinking). Sulfoniumsalt PAGs are preferred. Exemplary acid generators are described in JP-A2008-111103, paragraphs [0122] to [0142] (U.S. Pat. No. 7,537,880). Theacid generators may be used alone or in admixture of two or more. Wherea polymerizable PAG is copolymerized in a polymer, it is not alwaysnecessary to add the PAG.

An appropriate amount of the PAG added is 0.1 to 50 parts, morepreferably 0.5 to 40 parts by weight per 100 parts by weight of the basepolymer. With less than 0.1 part of PAG, the amount of acid generatedbecomes minimal, resulting in the exposed region having an insufficientalkali dissolution rate. If the amount of PAG exceeds 50 parts, a mixingphenomenon may occur as a result of acid migrating to the overlyingresist film.

To the silicon-containing intermediate film-forming composition, a basiccompound may be added. By adjusting the type and amount of basiccompound, the undercut and footing profiles of resist pattern may bemodified or corrected. Specifically, if a resist pattern is of footingprofile, the amount of a basic compound added is reduced; if a resistpattern is of undercut profile, the amount of a basic compound added isincreased.

The basic compound serves to improve contrast by trapping the acidgenerated by the acid generator to control acid diffusion. Exemplarybasic compounds include primary, secondary and tertiary amine compounds,specifically amine compounds having a hydroxyl, ether, ester, lactone,cyano or sulfonic ester group, as described in JP-A 2008-111103,paragraphs [0146] to [0164], and compounds having a carbamate group, asdescribed in JP 3790649. Onium salts such as sulfonium salts, iodoniumsalts and ammonium salts of sulfonic acids which are not fluorinated atα-position as described in JP-A 2008-158339 (US 20080153030) and similaronium salts of carboxylic acids as described in JP 3991462 may be usedas the quencher. Although onium salts of sulfonic acids which are notfluorinated at α-position and onium salts of carboxylic acids lackbasicity, they function as a quencher by salt exchange with a superstrong acid fluorinated at α-position to neutralize the α-positionfluorinated sulfonic acid.

The basic compound is preferably compounded in an amount of 0.001 to 15parts and more preferably 0.01 to 10 parts by weight per 100 parts byweight of the base polymer. Less than 0.001 part of the basic compoundmay achieve no addition effect whereas more than 15 parts may result intoo low a sensitivity.

The organic solvent which is used in each of the underlayer film-formingcomposition and the silicon-containing intermediate film-formingcomposition and resist composition combined therewith is notparticularly limited as long as the base resin, acid generator,crosslinker and other additives are soluble therein. Exemplary solventsinclude ketones such as cyclohexanone, cyclopentanone and methyl-2-amylketone; alcohols such as 3-methoxybutanol, 3-methyl-3-methoxybutanol,1-methoxy-2-propanol, and 1-ethoxy-2-propanol; ethers such as propyleneglycol monomethyl ether, ethylene glycol monomethyl ether, propyleneglycol monoethyl ether, ethylene glycol monoethyl ether, propyleneglycol dimethyl ether, and diethylene glycol dimethyl ether; esters suchas propylene glycol monomethyl ether acetate (PGMEA), propylene glycolmonoethyl ether acetate, ethyl lactate, ethyl pyruvate, butyl acetate,methyl 3-methoxypropionate, ethyl 3-ethoxypropionate, tert-butylacetate, tert-butyl propionate, and propylene glycol mono-tert-butylether acetate, which may be used alone or in admixture of two or more.Of these, diethylene glycol dimethyl ether, 1-ethoxy-2-propanol, ethyllactate, PGMEA and mixtures thereof are preferred for use in theunderlayer film-forming composition.

The organic solvent is preferably used in an amount of 200 to 10,000parts, more preferably 300 to 8,000 parts by weight per 100 parts byweight of the total base polymer(s).

Process

Another aspect of the invention is directed to a process for forming apattern in a substrate by lithography. In one embodiment, the patternforming process comprises the steps of applying the underlayerfilm-forming composition onto a substrate to form an underlayer film,forming a silicon-containing intermediate film on the underlayer film,applying a photoresist composition onto the intermediate film to form aresist film thereon, exposing a circuitry region of the resist film toradiation, developing it with a developer to form a resist pattern, dryetching the intermediate film with the resist pattern serving as mask,etching the underlayer film with the intermediate film serving as mask,and etching the substrate for thereby forming a pattern. In a modifiedembodiment, the process comprises substantially the same steps as aboveand later steps of implanting ions into the substrate with theunderlayer film serving as mask, and stripping the underlayer film inalkaline water. Where the exposed region of the intermediate film isdissolvable in alkaline developer, the step of dry etching theintermediate film with the resist pattern serving as mask may beskipped. Also, where the intermediate film is strippable in alkalinewater after dry etching of the substrate or after ion implantation intothe substrate, there is the advantage that the intermediate film can bestripped simultaneously with the underlayer film. The intermediate layermay also be stripped using an acid. In this case, the silicon-containingintermediate layer is stripped in a sulfuric acid/aqueous hydrogenperoxide solution or hydrochloric acid/aqueous hydrogen peroxidesolution, after which the underlayer film is stripped in alkaline water.

As the alkaline water for stripping the underlayer film, an ammoniumhydrogen peroxide solution which is a mixture of ammonia, aqueoushydrogen peroxide and water, commonly referred to as “SC1,” is mostpreferred. Also preferred as the alkaline water are aqueous solutionscontaining 1 to 99% by weight of ammonia, tetramethylammonium hydroxide(TMAH), choline hydroxide, DBU, DBN, hydroxylamine, and guanidine.

The underlayer film is formed on a substrate. The substrate may beselected from processable substrates, substrates subject to ionimplantation, such as Si, SiO₂, SiON, SiN, p-Si, α-Si, W, W—Si, Al, Cu,and Al—Si, various low-dielectric films, etch stopper films, and steppedsubstrates for the FinFET technology. The substrate typically has athickness of 10 to 10,000 nm, especially 20 to 5,000 nm.

Between the processable substrate and the underlayer film, a hard maskmay be disposed which helps to process the processable substrate. Thehard mask may be made of SiN, SiON, p-Si, α-Si, W, W—Si or amorphouscarbon when the processable substrate is a SiO₂ based insulating filmsubstrate; and SiO₂, SiN or SiON when the processable substrate is agate electrode such as p-Si, W—Si or Al—Si.

Referring to the underlayer film forming method, the underlayer film maybe formed on the substrate by any methods commonly used in the formationof photoresist film, such as spin coating. The underlayer film-formingcomposition is applied by such technique as spin coating, the organicsolvent is evaporated off to form a resist underlayer film, and theunderlayer film is desirably baked to promote crosslinking reaction toprevent intermixing with any resist film. The bake is preferably at atemperature of 80 to 300° C. for 10 to 300 seconds. The resistunderlayer film may have any desired thickness. The film thickness ispreferably in a range of 5 to 10,000 nm, especially 10 to 5,000 nm. Thefilm thickness may be selected from the range that ensures asatisfactory antireflective effect. After the resist underlayer film isformed, a silicon-containing intermediate film and a resist film areformed thereon in the case of the trilayer process.

When the trilayer process is applied, the silicon-containingintermediate film should preferably have optimum optical constants (m, kvalues) for antireflective effect, as described in JP-A 2006-293207,specifically a n value of 1.5 to 1.9, a k value of 0.15 to 0.3, and athickness of 20 to 130 nm. Likewise, the underlayer film has a n valueof 1.3 to 1.8, a k value of 0.2 to 0.8, and a thickness of at least 50nm.

In the photoresist composition for forming the resist film, basepolymers of well-known hydrocarbon components as described in JP-AH09-73173 and 2000-336121, for example, may be used. Although thethickness of the resist film is not particularly limited, it preferablyhas a thickness of 20 to 500 nm, more preferably 30 to 400 nm.

When the photoresist composition is applied to form the resist film,such techniques as spin coating are preferably used as is the case whenthe underlayer film is formed. After the photoresist composition isapplied as by spin coating, it is prebaked preferably at 80 to 180° C.for 10 to 300 seconds to form the resist film.

Subsequently, as in the standard technology, the process proceedsthrough steps of exposure of a circuitry region of the resist film toradiation, post-exposure bake (PEB), and development until a resistpattern is formed. Where a silicon-containing intermediate film isformed from a composition comprising a polymer having asilicon-containing acid labile group as pendant and an acid generator, apattern of the intermediate film is formed at the same time as theresist pattern is formed via exposure and development.

A resist protective film may be applied on top of the resist film. Theresist protective film may have an antireflective function as well andbe made of either water-soluble or water-insoluble material. Thewater-insoluble materials include a first class of materials dissolvablein alkaline developer and a second class of materials not dissolvable inalkaline developer, but strippable in fluorinated solvents. From theprocess aspect, the first class of materials is advantageous in that itcan be stripped at the same time as development of the resist film.Where the immersion lithography is applied, a protective film isprovided in some cases for the purposes of preventing acid generator andother additives from being leached out of the resist film, and improvingwater slip. The protective film should preferably have the nature thatit is not dissolved in water, but in alkali. Thus the preferredprotective film-forming material is a solution having a polymer withα-trifluoromethylhydroxy group dissolved in a higher alcohol of at least4 carbon atoms or an ether compound of 8 to 12 carbon atoms. Theprotective film is formed by spin coating the solution onto the prebakedresist film and prebaking. The protective film preferably has athickness of 10 to 200 nm. The dry or immersion exposure is followed byPEB and development in an alkaline developer for 10 to 300 seconds. Asthe alkaline developer, a 2.38 wt % tetramethylammonium hydroxide (TMAH)aqueous solution is widely used. Where a protective film soluble indeveloper is used, stripping of the protective film and development ofthe resist film can be conducted at the same time.

If residual water is on the resist film prior to PEB, the waterfunctions to suck up the acid from within the resist film during PEB,with a failure of pattern formation. For the purpose of completelyremoving water on the resist film prior to PEB, it is necessary to dryor recover water on the film by suitable means, for example, spin dryingprior to PEB, purging the film surface with dry air or nitrogen, oroptimizing the water recovery nozzle configuration or water recoveryprocess at a post-exposure stage.

Development may be carried out in an alkaline aqueous solution by such atechnique as puddle or dip technique. Preferably puddle development iscarried out in a 2.38 wt % aqueous solution of TMAH, typically at roomtemperature for 10 to 300 seconds. The structure is then rinsed withdeionized water and dried by spin drying, nitrogen blow or the like.During alkaline development, the exposed region of the positive resistfilm is dissolved away, and preferably the exposed region of thesilicon-containing intermediate film is simultaneously dissolved away.

If the size of the resist pattern as developed deviates from the desiredsize, it is necessary to form a new resist pattern by stripping theresist film, and coating a second resist film, followed by a second setof exposure and development. In this case, problems arise if only theresist film is stripped. Namely, when the second resist film is coatedand patterned, problems like footing of the second resist pattern and achange of sensitivity arise because the silicon-containing intermediatefilm has been affected by the first set of exposure and development. Itis then necessary to strip not only the resist film, but also thesilicon-containing intermediate film. Where the resist film and thesilicon-containing intermediate film are stripped, sometimes theunderlayer film can be damaged whereby the thickness of the underlayerfilm is reduced. If the thickness of the underlayer film is reduced,then it fails to exert necessary dry etch resistance. It is thusconcluded desirable that all films including from the resist film to theunderlayer film are stripped off.

Since the silicon-containing intermediate layer comes in contact withthe alkaline developer during development of the resist film, it musthave alkali resistance enough to withstand any film thickness loss bythe developer. This suggests that it is difficult to strip theintermediate layer in an alkaline solution. With respect to strippingafter the formation of a resist pattern by development, in a commonpractice, the resist film is stripped by dry ashing with oxygen gas, andthe silicon-containing intermediate layer is stripped by dry etchingwith fluorocarbon base gas or using an acid solution.

While the resist pattern after exposure and development and theunderlying silicon-containing intermediate film serve as mask, thehydrocarbon-based underlayer film is etched, typically by a dry etchingtechnique. In the case of the silicon-containing intermediate film ofthe type wherein the exposed region is not dissolved in alkalinedeveloper, the silicon-containing intermediate film must be processedwith fluorocarbon gas while the resist pattern serves as mask. This stepmay be skipped in the case of the intermediate film of the type whereinthe exposed region turns soluble in alkaline developer under the actionof acid. Dry etching of the underlayer film is carried out with oxygengas or hydrogen gas, to which He, Ar, another inert gas, CO, CO₂, NH₃,SO₂, N₂, or NO₂ gas may be added. The substrate is then processed byetching. Etching is carried out with a gas composed mainly offluorocarbon gas when the substrate is SiO₂ or SiN, and with a gascomposed mainly of chlorine or bromine gas when the substrate ispolysilicon (p-Si), Al or W. In the case of ion implantation, processingof the substrate is not necessarily needed. Ions are implanted into thesubstrate while the underlayer film pattern serves as mask. At the endof ion implantation, the silicon-containing intermediate film and theunderlayer film are stripped off. Particularly when thesilicon-containing intermediate film has been crosslinked via acetal ofvinyl ether, the intermediate film can be stripped with sulfuric acid orhydrochloric acid because the bond is decomposable with acid. Thestripper solution may contain aqueous hydrogen peroxide. Thesilicon-containing intermediate film may also be stripped by dry etchingwith fluorocarbon gas.

Next, the underlayer film is stripped. In alkaline water at pH 9 orabove, hydroxycoumarin opens its ring to generate a carboxyl group sothat the film becomes readily dissolvable in alkaline water. SPMsolution which is a mixture of sulfuric acid and aqueous hydrogenperoxide is a strong stripper capable of dissolving cured organic films.However, where the substrate is a silicon substrate, for example, thesolution forms an oxide film on the substrate surface. If anelectrically insulating layer in the form of silicon oxide film isformed on the surface of the ion implanted silicon substrate, itinhibits electron migration and so semiconductor performance isdegraded. It is thus concluded that an underlayer film which isstrippable with a peroxide-free stripper is preferable. Alkaline waterdoes not form an oxide film on the substrate surface.

The alkaline water which can be used as the stripper is an aqueoussolution containing 1 to 99% by weight of at least one member selectedfrom the group consisting of ammonia, ammonia hydrogen peroxide water(i.e., mixture of ammonia, aqueous hydrogen peroxide and water),tetramethylammonium hydroxide (TMAH), tetraethylammonium hydroxide,tetrapropylammonium hydroxide, tetrabutylammonium hydroxide, cholinehydroxide, benzyltrimethylammonium hydroxide, benzyltriethylammoniumhydroxide, DBU, DBN, hydroxylamine, 1-butyl-1-methylpyrrolidiniumhydroxide, 1-propyl-1-methylpyrrolidinium hydroxide,1-butyl-1-methylpiperidinium hydroxide, 1-propyl-1-methylpiperidiniumhydroxide, mepiquathydroxide, trimethylsulfonium hydroxide, hydrazines,ethylenediamines, and guanidines.

The stripping step is typically at a temperature of 10 to 100° C. for 10to 30 minutes. Heating accelerates the stripping rate, but causes moredamage to the substrate. It is thus necessary to find an optimum balanceof stripper concentration, stripping time and temperature. At the end ofstripping, the substrate is cleaned with deionized water to remove thestripper and dried. Before or after stripping with alkaline water, astripper solution of acidic water such as SP2 or SPM may also be used.

FIGS. 1 and 2 illustrate the pattern forming process in one embodimentof the invention. In FIG. 1 (A), a hydrocarbon underlayer film 20 isformed on a substrate 10. If desired, a silicon-containing intermediatefilm 30 is formed thereon, as shown in (B), and a resist film 40 isformed thereon, as shown in (C). In (D), the selected region of theresist film 40 is exposed to radiation. In FIG. 2 (E), the resist film40 is PEB and developed to form a resist pattern. In this embodiment,the exposed region of resist film 40 and underlying silicon-containingintermediate film 30 are dissolved during development. In (F), theunderlayer film 20 is processed by dry etching with H₂ gas while theintermediate film serves as mask. In (G), ions are implanted into thebare region of substrate 10 while the underlayer film 20 serves as mask.The ion-implanted region of substrate is depicted at 10b. Finally, thetrilayer is stripped off, leaving the substrate 10 having ion-implantedregions 10b as shown in (H).

EXAMPLE

Examples of the invention are given below by way of illustration and notby way of limitation.

Synthesis Example Synthesis of Novolak Resin

A lactone ring-containing phenol corresponding to formula (1) wascombined with a co-condensable compound, 37 wt % formalin, and oxalicacid, which was stirred at 100° C. for 24 hours. At the end of reaction,the reaction product was poured into 500 ml of methyl isobutyl ketone,which was thoroughly washed with water to remove the catalyst and metalimpurities. The solvent was removed under reduced pressure. The systemwas further evacuated to 2 mmHg at 150° C., for removing water andunreacted monomers. In this way, Novolak Resins 1 to 22 and ComparativeNovolak Resins 1 to 3 were similarly prepared except the followingchanges.

Novolak Resin 6 was prepared using 6-hydroxy-2-naphthaldehyde instead of37 wt % formalin. Novolak Resin 7 was prepared using3-furancarboxyaldehyde instead of 37 wt % formalin. Novolak Resin 8 wasprepared using 3-thiophene aldehyde instead of 37 wt % formalin. NovolakResin 13 was prepared using a 50 wt % dioxane solution of Aldehyde 1(shown below) instead of 37 wt % formalin. Novolak Resin 14 was preparedusing a 50 wt % dioxane solution of Aldehyde 2 (shown below) instead of37 wt % formalin. Novolak Resin 15 was prepared using a 50 wt % dioxanesolution of Aldehyde 3 (shown below) instead of 37 wt % formalin.Novolak Resin 16 was prepared using a 50 wt % dioxane solution ofAldehyde 4 (shown below) instead of 37 wt % formalin. Novolak Resin 17was prepared using a 50 wt % dioxane solution of Aldehyde 5 (shownbelow) instead of 37 wt % formalin. Novolak Resin 18 was prepared usinga 50 wt % dioxane solution of Aldehyde 6 (shown below) instead of 37 wt% formalin.

The crosslinker, acid generator, quencher and solvent used in Examplesare identified below.

Crosslinker:

Thermal Acid Generator:

Photoacid Generator:

Quencher:

Organic Solvent:

PGMEA (propylene glycol monomethyl ether acetate)

CyH (cyclohexane)

Examples and Comparative Examples Preparation of Underlayer Film-FormingComposition

Resist underlayer film-forming compositions (Examples 1 to 22 andComparative Examples 1 to 3) were prepared by dissolving Novolak Resins1 to 22 and Comparative Novolak Resins 1 to 3, acid generator TAG1, andCrosslinkers 1 to 4 in an organic solvent according to the formulationshown in Table 1 and filtering through a fluoro-resin filter with a poresize of 0.1 μm. The organic solvent contained 0.1 wt % of surfactantFC-4430 (3M-Sumitomo Co., Ltd.).

Each of the compositions in solution form was coated onto a siliconsubstrate and baked at 200° C. for 60 seconds to form a resistunderlayer (antireflective) film of 100 nm thick (Underlayer films 1 to22 and Comparative underlayer films 1 to 3). Using a variable anglespectroscopic ellipsometer (VASE®) of J. A. Woollam Co., the underlayerfilms were measured for optical constants (refractive index n,extinction coefficient k) at wavelength 193 nm. The results are alsoshown in Table 1.

TABLE 1 Acid Organic Polymer generator Crosslinker solvent (pbw) (pbw)(pbw) (pbw) n k Example 1 Underlayer Novolak Resin 1 — Crosslinker 1PGMEA 1.40 0.58 film 1 (100) (20) (2,500) 2 Underlayer Novolak Resin 2 —Crosslinker 2 PGMEA 1.41 0.50 film 2 (100) (20) (2,500) 3 UnderlayerNovolak Resin 3 TAG1 Crosslinker 3 PGMEA 1.42 0.49 film 3 (100) (2.0)(20) (2,500) 4 Underlayer Novolak Resin 4 TAG1 Crosslinker 4 PGMEA 1.380.60 film 4 (100) (2.0) (20) (2,500) 5 Underlayer Novolak Resin 5 TAG1Crosslinker 4 PGMEA 1.45 0.46 film 5 (100) (2.0) (20) (2,500) 6Underlayer Novolak Resin 6 TAG1 Crosslinker 4 PGMEA 1.45 0.42 film 6(100) (2.0) (20) (2,500) 7 Underlayer Novolak Resin 7 TAG1 Crosslinker 4PGMEA 1.49 0.51 film 7 (100) (2.0) (20) (2,500) 8 Underlayer NovolakResin 8 TAG1 Crosslinker 4 PGMEA 1.55 0.52 film 8 (100) (2.0) (20)(2,500) 9 Underlayer Novolak Resin 9 TAG1 Crosslinker 4 PGMEA 1.45 0.46film 9 (100) (2.0) (20) (2,500) 10 Underlayer Novolak Resin 10 TAG1Crosslinker 4 PGMEA 1.40 0.63 film 10 (100) (2.0) (20) (2,500) 11Underlayer Novolak Resin 11 TAG1 Crosslinker 4 PGMEA 1.42 0.59 film 11(100) (2.0) (20) (2,500) 12 Underlayer Novolak Resin 12 TAG1 Crosslinker4 PGMEA 1.40 0.58 film 12 (100) (2.0) (20) (2,500) 13 Underlayer NovolakResin 13 TAG1 Crosslinker 4 PGMEA 1.41 0.45 film 13 (100) (2.0) (20)(2,500) 14 Underlayer Novolak Resin 14 TAG1 Crosslinker 4 PGMEA 1.480.42 film 14 (100) (2.0) (20) (2,500) 15 Underlayer Novolak Resin 15TAG1 Crosslinker 4 PGMEA 1.47 0.44 film 15 (100) (2.0) (20) (2,500) 16Underlayer Novolak Resin 16 TAG1 Crosslinker 4 PGMEA 1.44 0.51 film 16(100) (2.0) (20) (2,500) 17 Underlayer Novolak Resin 17 TAG1 Crosslinker4 PGMEA 1.48 0.51 film 17 (100) (2.0) (20) (2,500) 18 Underlayer NovolakResin 18 TAG1 Crosslinker 4 PGMEA 1.39 0.61 film 18 (100) (2.0) (20)(2,000) CyH (500) 19 Underlayer Novolak Resin 19 TAG1 Crosslinker 4PGMEA 1.50 0.48 film 19 (100) (2.0) (20) (2,500) 20 Underlayer NovolakResin 20 TAG1 Crosslinker 4 PGMEA 1.48 0.51 film 20 (100) (2.0) (20)(2,500) 21 Underlayer Novolak Resin 21 TAG1 Crosslinker 4 PGMEA 1.550.48 film 21 (100) (2.0) (20) (2,500) 22 Underlayer Novolak Resin 22TAG1 Crosslinker 4 PGMEA 1.51 0.50 film 22 (100) (2.0) (20) (2,500)Comparative 1 Comparative Comparative TAG1 Crosslinker 4 PGMEA 1.40 0.36Example underlayer Novolak Resin 1 (2.0) (20) (4,000) film 1 (100) 2Comparative Comparative TAG1 Crosslinker 4 PGMEA 1.39 0.69 underlayerNovolak Resin 2 (2.0) (20) (4,000) film 2 (100) 3 ComparativeComparative TAG1 Crosslinker 4 PGMEA 1.42 0.61 underlayer Novolak Resin3 (2.0) (20) (4,000) film 3 (100)

As seen from Table 1, the resist underlayer films of Examples 1 to 22have a refractive index (n) in the range of 1.3 to 1.6 and an extinctioncoefficient (k) in the range of 0.3 to 0.7, that is, optimum opticalconstants to exert a satisfactory antireflective effect at a filmthickness of at least 30 nm.

Preparation of Intermediate Film-Forming Composition

A silicon-containing intermediate film-forming composition was preparedby dissolving a resin, i.e., Silicon-containing polymer 1 (shown below),acid generator PAG2, quencher, and Crosslinker 1 in an organic solventaccording to the formulation shown in Table 2 and filtering through afluoro-resin filter with a pore size of 0.1 μm. The organic solventcontained 0.1 wt % of surfactant FC-4430 (3M-Sumitomo Co., Ltd.).

The composition in solution form was coated onto a silicon substrate andbaked at 200° C. for 60 seconds to form a silicon-containingintermediate film 1 of 40 nm thick. Using a variable angle spectroscopicellipsometer (VASE®) of J. A. Woollam Co., the silicon-containingintermediate film 1 was measured for optical constants (refractive indexn, extinction coefficient k) at wavelength 193 nm. The results are alsoshown in Table 2.

TABLE 2 Acid gen- Quench- Cross- Polymer erator er linker Organic (pbw)(pbw) (pbw) (pbw) solvent n k Silicon- Silicon- PAG 2 Quench- Cross-PGMEA 1.61 0.33 containing containing (7.0) er linker (4,000) inter-polymer 1 2 1 mediate (100) (2.0) (20) film 1 Silicon-containing polymer1 Mw = 8,900 Mw/Mn = 1.88

Preparation of ArF Resist Film-Forming Composition

An ArF resist to player film-forming composition was prepared bydissolving Resist Polymer 1 (shown below), acid generator PAG1, andquencher in an organic solvent according to the formulation shown inTable 3 and filtering through a fluoro-resin filter with a pore size of0.1 μm. The organic solvent contained 0.1 wt % of surfactant FC-4430(3M-Sumitomo Co., Ltd.).

TABLE 3 Polymer Acid generator Quencher Solvent (pbw) (pbw) (pbw) (pbw)ArF resist 1 Resist Polymer 1 PAG 1 Quencher 1 PGMEA (100) (8.0) (2.0)(2,000) Resist Polymer 1 Mw = 7,500 Mw/Mn = 1.92

Preparation of Ammonia Hydrogen Peroxide Solution SC1

A solution SC1 was prepared by mixing ammonia, aqueous hydrogen peroxideand water in a ratio of 1:1:5.

Preparation of Hydrochloric Acid Hydrogen Peroxide Solution SC2

A solution SC2 was prepared by mixing hydrochloric acid, aqueoushydrogen peroxide and water in a ratio of 1:1:5.

Each of the underlayer film-forming compositions in solution form(Examples 1 to 22 and Comparative Examples 1 to 3) was coated onto asilicon substrate and baked at 200° C. for 60 seconds to form anunderlayer film of 100 nm thick (Underlayer films 1 to 22 andComparative underlayer films 1 to 3). As a test for examining whether ornot the film was strippable in ammonia hydrogen peroxide solution, thesilicon substrates in Examples 1 to 22 and Comparative Examples 1 to 3were immersed in ammonia hydrogen peroxide solution SC1 at 70° C. for 5minutes, after which the thickness of the underlayer film was measured.Similarly, the coated substrate in Example 23 was immersed in 10 wt %TMAH aqueous solution at 23° C. for 5 minutes, and the coated substratein Example 24 was immersed in 25 wt % TMAH aqueous solution at 23° C.for 1 minute, for examining whether or not the film was strippable inthe relevant solution. The results are shown in Table 4.

TABLE 4 Film thickness after wafer immersion (nm) Example 1 Underlayerfilm 1 0 2 Underlayer film 2 0 3 Underlayer film 3 0 4 Underlayer film 40 5 Underlayer film 5 0 6 Underlayer film 6 0 7 Underlayer film 7 0 8Underlayer film 8 0 9 Underlayer film 9 0 10 Underlayer film 10 0 11Underlayer film 11 0 12 Underlayer film 12 0 13 Underlayer film 13 0 14Underlayer film 14 0 15 Underlayer film 15 0 16 Underlayer film 16 0 17Underlayer film 17 0 18 Underlayer film 18 0 19 Underlayer film 19 0 20Underlayer film 20 0 21 Underlayer film 21 0 22 Underlayer film 22 0 23Underlayer film 1 0 24 Underlayer film 1 0 Comparative 1 Comparativeunderlayer film 93 Example 1 2 Comparative underlayer film 98 2 3Comparative underlayer film 99 3

As seen from Table 4, Underlayer films 1 to 22 are strippable in ammoniahydrogen peroxide solution SC1 whereas Comparative underlayer films 1 to3 are not strippable because the majority of film is left afterimmersion.

Pattern Etching Test

Each of the underlayer film-forming compositions in solution form(Examples 1 to 22 and Comparative Example 1) was coated onto a siliconwafer substrate and baked at 200° C. for 60 seconds to form anunderlayer film of 100 nm thick (Underlayer films 1 to 22 andComparative underlayer film 1). The silicon-containing intermediatefilm-forming composition in solution form was coated on the underlayerfilm and baked at 200° C. for 60 seconds to form an intermediate film of40 nm thick. The ArF resist to player film-forming composition insolution form was coated on the intermediate film and baked at 105° C.for 60 seconds to form a photoresist film of 100 nm thick.

Using an ArF immersion stepper model NSR-S610C (Nikon Corp., NA 1.30, σ0.98/0.65, 35° dipole/s-polarized illumination), the coated substratewas exposed through a 6% halftone phase shift mask. The resist film wasbaked (PEB) at 100° C. for 60 seconds and then developed in a 2.38 wt %TMAH aqueous solution for 30 seconds to form a positive 45 nm 1:1line-and-space pattern. Since the silicon-containing intermediate filmused herein is of the type wherein the exposed region turns dissolvablein alkaline developer, a pattern of silicon-containing intermediate filmwas formed as a result of development at the same time as the resistpattern.

The structure was dry etched using an etching instrument Telius by TokyoElectron, Ltd. Specifically, the underlayer film was processed with thesilicon-containing intermediate film made mask.

Transfer Conditions of Intermediate Film to Underlayer Film

Chamber pressure 2.0 Pa RF power 500 W Ar gas flow rate 30 ml/min H₂ gasflow rate 60 ml/min Time 180 sec

The film patterns in cross section were observed under electronmicroscope S-4700 (Hitachi, Ltd.) to compare their profile.

Thereafter, the silicon-containing intermediate film was stripped byimmersion in SC2 at 60° C. for 3 minutes, and the underlayer film wasstripped by immersion in SC1 at 70° C. for 3 minutes. The results areshown in Table 5.

TABLE 5 ArF resist Resist Residual Underlayer Silicon-containingtoplayer profile Underlayer film after film intermediate film film asdeveloped film profile stripping Example 1 Underlayer Silicon-containingArF Perpendicular Perpendicular No residual film 1 intermediate layer 1resist 1 2 Underlayer Silicon-containing ArF Perpendicular PerpendicularNo residual film 2 intermediate layer 1 resist 1 3 UnderlayerSilicon-containing ArF Perpendicular Perpendicular No residual film 3intermediate layer 1 resist 1 4 Underlayer Silicon-containing ArFPerpendicular Perpendicular No residual film 4 intermediate layer 1resist 1 5 Underlayer Silicon-containing ArF Perpendicular PerpendicularNo residual film 5 intermediate layer 1 resist 1 6 UnderlayerSilicon-containing ArF Perpendicular Perpendicular No residual film 6intermediate layer 1 resist 1 7 Underlayer Silicon-containing ArFPerpendicular Perpendicular No residual film 7 intermediate layer 1resist 1 8 Underlayer Silicon-containing ArF Perpendicular PerpendicularNo residual film 8 intermediate layer 1 resist 1 9 UnderlayerSilicon-containing ArF Perpendicular Perpendicular No residual film 9intermediate layer 1 resist 1 10 Underlayer Silicon-containing ArFPerpendicular Perpendicular No residual film 10 intermediate layer 1resist 1 11 Underlayer Silicon-containing ArF PerpendicularPerpendicular No residual film 11 intermediate layer 1 resist 1 12Underlayer Silicon-containing ArF Perpendicular Perpendicular Noresidual film 12 intermediate layer 1 resist 1 13 UnderlayerSilicon-containing ArF Perpendicular Perpendicular No residual film 13intermediate layer 1 resist 1 14 Underlayer Silicon-containing ArFPerpendicular Perpendicular No residual film 14 intermediate layer 1resist 1 15 Underlayer Silicon-containing ArF PerpendicularPerpendicular No residual film 15 intermediate layer 1 resist 1 16Underlayer Silicon-containing ArF Perpendicular Perpendicular Noresidual film 16 intermediate layer 1 resist 1 17 UnderlayerSilicon-containing ArF Perpendicular Perpendicular No residual film 17intermediate layer 1 resist 1 18 Underlayer Silicon-containing ArFPerpendicular Perpendicular No residual film 18 intermediate layer 1resist 1 19 Underlayer Silicon-containing ArF PerpendicularPerpendicular No residual film 18 intermediate layer 1 resist 1 20Underlayer Silicon-containing ArF Perpendicular Perpendicular Noresidual film 18 intermediate layer 1 resist 1 21 UnderlayerSilicon-containing ArF Perpendicular Perpendicular No residual film 18intermediate layer 1 resist 1 22 Underlayer Silicon-containing ArFPerpendicular Perpendicular No residual film 18 intermediate layer 1resist 1 Comparative 1 Comparartive Silicon-containing ArF PerpendicularPerpendicular intermediate Example underlayer intermediate layer 1resist 1 film was film 1 stripped, but not underlayer film

Japanese Patent Application No. 2013-122866 is incorporated herein byreference.

Although some preferred embodiments have been described, manymodifications and variations may be made thereto in light of the aboveteachings. It is therefore to be understood that the invention may bepracticed otherwise than as specifically described without departingfrom the scope of the appended claims.

The invention claimed is:
 1. A photoresist underlayer film-formingcomposition for use in lithography, comprising a novolak resincomprising recurring units having the general formula (1):

wherein R¹ is hydrogen, an acid labile group, glycidyl group, or astraight, branched or cyclic C₁-C₁₀ alkyl, acyl or alkoxycarbonyl, R² ishydrogen, or a straight, branched or cyclic C₁-C₁₀ alkyl, C₂-C₁₀alkenyl, or C₆-C₁₀ aryl group, which may have a hydroxyl, alkoxy,acyloxy, ether, sulfide or halogen moiety, or a halogen atom, hydroxyl,acyl, carboxyl, acyloxy, alkoxycarbonyl, cyano or C₁-C₄ alkoxy group, R³is hydrogen, or a straight, branched or cyclic C₁-C₆ alkyl, a straight,branched or cyclic C₂-C₁₀ alkenyl, or C₆-C₁₂ aryl group, which may havea hydroxyl, alkoxy, ether, thioether, carboxyl, alkoxycarbonyl, acyloxy,—COOR or —OR moiety, wherein R is a lactone ring, acid labile group, or—R′—COOR″, wherein R′ is a single bond or alkylene group, and R″ is anacid labile group, X is methylene, ethylene, ethynylene, —S— or —NH—,each of m and n is 1 or 2, wherein the novolak resin is obtained bycondensation reaction of a monomer with an aldehyde, said monomer beingselected from the group consisting of the following formulae,


2. The underlayer film-forming composition of claim 1, furthercomprising an organic solvent.
 3. The underlayer film-formingcomposition of claim 2, further comprising an acid generator.
 4. Theunderlayer film-forming composition of claim 2, further comprising acrosslinker.
 5. The underlayer film-forming composition of claim 4wherein the crosslinker is selected from the group consisting ofmelamine compounds, guanamine compounds, glycoluril compounds and ureacompounds having substituted thereon at least one group selected fromamong methylol, alkoxymethyl and acyloxymethyl groups, epoxy compounds,isocyanate compounds, azide compounds, and compounds having an alkenylether group.
 6. The underlayer film-forming composition of claim 1wherein the aldehyde is selected from the group consisting offormaldehyde, trioxane, paraformaldehyde, benzaldehyde,methoxybenzaldehyde, phenylbenzaldehyde, tritylbenzaldehyde,cyclohexylbenzaldehyde, cyclopentylbenzaldehyde, tert-butylbenzaldehyde,naphthalene aldehyde, hydroxynaphthalene aldehyde, anthracene aldehyde,fluorene aldehyde, pyrene aldehyde, methoxynaphthalene aldehyde,dimethoxynaphthalene aldehyde, acetaldehyde, propyl aldehyde,phenylacetaldehyde, naphthalene acetaldehyde, substituted orunsubstituted carboxynaphthalene acetaldehyde, α-phenylpropyl aldehyde,β-phenylpropyl aldehyde, o-hydroxybenzaldehyde, m-hydroxybenzaldehyde,p-hydroxybenzaldehyde, o-chlorobenzaldehyde, m-chlorobenzaldehyde,p-chlorobenzaldehyde, o-nitrobenzaldehyde, m-nitrobenzaldehyde,p-nitrobenzaldehyde, o-methylbenzaldehyde, m-methylbenzaldehyde,p-methylbenzaldehyde, p-ethylbenzaldehyde, p-n-butylbenzaldehyde,furfural, furancarboxyaldehyde, thiophene aldehyde, and aldehydesrepresented by the following formulae,